Purpose: This stress analysis in vitro study was used to evaluate the effect of blocking ring spacer used during picking up the female housing of ball attachment used for retaining mandibular 4- implants assisted complete overdenture. Materials and Methods: Epoxy resin model representing a completely edentulous mandibular ridge was used. The model received four implants inserted at canine and first molar area bilaterally. The residual ridge and the retromlar regions for epoxy resin model was covered by resilient soft liner to simulate the oral mucosa. The study groups were classified according to using of blocking ring spacerinto two groups: Group I: the female housing of ball attachment was picked up with using of blocking ring spacer. Group II: the female housing of ball attachment was picked up without using of blocking ring spacer. Four linear strain gauges were inserted in to the epoxy resin at 2mm  mesial, distal, buccal and lingual to each implant in order to monitor the strain around the implants on loading and non-loading sides during unilateral and bilateral load application. The results:when compared the stresses during unilateral loading in the loading side between groups, for anterior implants, group II recorded significant higher stresses than group I. For posterior implants, group II recorded significant higher stresses than group I. when compared the stresses between implant positions: For both group there was no significant difference between implant positions.  Conclusions:Regarding stress analysis, using of blocking ring spacer is recommended during pick up procedure of female housings of ball attachments used for retaining 4-implants mandibular complete overdenture to minimize the peri-implant stresses.